The default for the color setting has been changed to override never, so you need to change the color setting to respecting High Contrast Mode.

• Settings -> General: Fonts & Colors -> Colors: "Override the colors specified by the page with your selections above" -> "Only with High Contrast themes"

Thanks cor-el. You got me looking in the in the right place. Using "Only with High Contrast themes" didn't work, but when I selected "use system colors" and override "always" it works for me.

Is there any plan to consider this as a bug? Frankly, it isn't very good accessibility design to require users to dig through obscure settings menus in order to enable assistive technology. Not to mention, most won't know to do this unless they find this question.